If a ritually clean thing touches a najis thing and if either or both of them are so wet that the wetness of one reaches the other, the clean thing will become najis.
Do ointment, cream and similar materials transmit impurity? What about liquids other than water?
All Shia scholars (Mujtahedeen) say: “If a ritually clean thing touches a najis thing and if either or both of them are so wet that the wetness of one reaches the other, the clean thing will become najis. And if the wetness is so little that it does not transfer to the other object, the thing that has been ritually pure does not become najis.
As well, if a ritually clean thing touches a najis thing and one doubts whether either or both of them were wet or not, the ritually pure thing does not become najis.
Transmission of impurity (najasah) through cream, ointment and liquids other than water is possible.
Source: http://www.islamquest.net/en/archive/question/fa3758